"Sebastian came through his final work well with his lead horse Florid over seven furlongs on the trial ground this morning," Cecil said. "However, he was found to be sore across his back after returning to the yard.''
The trainer said the colt would take his chance at Epsom only if he is sound this morning, when the final declarations for the Derby have to be made.
"Unless he is normal by tomorrow morning, he will be unable to run on Saturday," were Cecil's words.
Sebastian, owned by Lord Howard de Walden, who won the Derby with Slip Anchor 10 years ago, was the subject of a large-scale gamble following a 10-length victory in a minor event at Salisbury last month.
Initially quoted at 25-1 by William Hill after that race, he had been backed into 9-2 third favourite by the start of this week. The firm has now eased Sebastian's price out to 9-1, with the favourite, Pennekamp, cut to 11-10, and Spectrum left on 3-1. The colt is also a 9-1 chance with Coral, but has been deleted from the betting by Ladbrokes.
Some bookmakers introduced a ''non-runner, no bet'' concession for the Derby earlier this week. But, if Sebastian is withdrawn, those new terms will have come too late to save most money put on the colt.
Wet weather at Epsom yesterday is unlikely to have improved the chance of Celtic Swing lining up on Saturday. His owner, Peter Savill, has stated that last Sunday's winner of the Prix du Jockey-Club will run in the Derby only if the ground becomes soft.
Yesterday's showers failed to alter the state of the going. The racecourse manager, Andrew Cooper, said: "We had some rain this morning between 8am and 10am but it was not an appreciable amount. The ground remains good and the forecast is for it to get brighter from tomorrow."
A decision on whether outsider Korambi will take his chance has been deferred until today. The participation of the Clive Brittain-trained colt, quoted at 200-1 by William Hill, hinges on the state of the ground.
"We will make a decision tomorrow morning by declaration time," Brittain said yesterday.